The primary purpose of the proposed studies is to examine the mechanisms whereby various metabolic substrates may affect renal transport processes. Metabolic substrates may affect renal transport processes by: 1. contributing to the supply of energy available to perform the work of transport. 2. participating directly in the co-transport of other solutes. 3. affecting the metabolic and other processes involved in maintaining the integrity and permeability characteristics of cellular and paracellular pathways. These studies will measure transport and metabolic events simultaneously at the segmental rather than organ level and during the transporting rather than collapsed or resting states. Microfluorometry is used to monitor changes in the redox level of mitochondrial NAD in various preparations of transporting renal epithelia including rabbit tubules isolated and perfused in vitro. The application of two independent techniques (microfluorometry and measurements of transport) to specific areas of the kidney will provide the first direct correlations between changes in renal transport and metabolism. Important parallel studies will be performed to establish the biochemical basis of the fluorometric signals by direct measurements of ATP, ADP, oxygen consumption and spectrophotometric assay of cytochrome redox levels. These parallel studies will provide the factual and conceptual framework upon which the microfluorometric data may be interpreted. In this manner, we expect to separate the various effects of metabolic substrates on renal transport processes from each other. These studies will also provide quantitative information which will hopefully enable us to determine the nature of the cytoplasmic signal linking changes in membrane transport to changes in mitochondrial function, and vice versa.